1. Field of the Invention
The present invention relates generally to tea extracts which are stabilized for long-term preservation and a method of producing the same, and more particularly, to tannin containing tea extracts not allowing creation of any precipitates during long-term preservation, as well as a method of producing the same.
2. Description of the Related Art
Tea extracts, which contain tannin, such as black tea, green tea, and oolong tea are obtained by extracting tea leaves with hot water, followed by treating the crude extracts, for example, by filtration, refrigeration, and centrifugation to remove small particles of tea leave and insoluble solid matter to consume as goods to drink directly from cans or PET containers, or after dilution of sterile thick extracts which are packed in paper containers and BIB (bag-in-box) containers and as thick extracts which are packed and frozen in 20-L cans or drums for raw material.
These extracts, however, contain caffeine, proteins, and polysaccharides, all of which combine with tannin contained by heating during production, air temperature change during preservation, temperature change during refrigeration and freezing, and by time, to form aggregates or precipitates, deteriorate their commercial value visually, and change by their taste because of precipitation of bitter components.
These phenomena occur especially in thick tea extracts. When tea extracts which are packed, for example, in drums for raw material are diluted to produce, for example, drinks, many steps such as filtration and centrifugation can be needed to remove insoluble solid matter formed, yield is lowered to remove precipitates, and important components for taste might be removed. If tannin and/or caffeine are/is removed, characteristic flavor and/or bitter taste can be lost, and balance of components might be damaged.
Precipitates can damage commercial value in the following ways: 1) Precipitates can damage by turbidness or precipitates visually and/or by giving misunderstanding that the goods are contaminated. 2) In case a thick tea extract is diluted to drink, taste and color of the obtained diluted extract can vary with the amount of precipitates. 3) When tea extracts are filled in containers, precipitates formed can narrow the outlet port, so that the filling amount can be lowered.
Therefore, the following methods have been proposed as methods for producing tea extracts by preventing generation of precipitates during long-term preservation: Tea extracts have been treated with tannase, cellulase, hemicellulase, xylanase, and/or pectinase, followed by removing precipitates using a cation-exchange resin (See Japan Patent Laid-Open S50-154462). To tea extracts is added ascorbic acid to lower the pH, the resulting mixture is chilled, and precipitates formed are removed, for example, by centrifugation, followed by neutralizing the pH (See Japan Patent Laid-Open H4-311348). The pH of a tea extract is lowered, the obtained mixture is chilled rapidly, to which are added oxidase and tannase, and the obtained mixture is incubated to remove precipitates (See Japan Patent Laid-Open H7-303450).
Each of the above-mentioned methods, however, is not enough to prevent formation of precipitates during treatments such as heating and freezing and long-term preservation or during circulation, especially for thick tea extracts which are diluted to drink.
In addition, formation of precipitates depends on the quality of the raw material tea leaves, the concentration of the tea extract, and the condition during preservation, so that removing the precipitates can cause production of ununiform products with respect to taste and turbidness. Therefore, removing the precipitates does not contribute to stabilize the quality of products.
It is therefore the object of the present invention to solve these problems, which could be successfully achieved.
The applicant(s) found that formation of precipitates is remarkably prevented by adding carrageenan to tea extracts, and that if this method is combined with prior arts such as precipitate-removing by refrigeration and treatment with tannase, turbidness or precipitate is not formed even under severer conditions.
The present invention comprises adding carrageenan to tea extracts which contain tannin, by which insolubilization of proteins and polysaccharides which are contained in the tea extracts by heating and freezing, and/or aggregation of proteins and polysaccharides with tannin, for example, during long-term preservation can be prevented, wherein carrageenan is added for the action different from prevention of physical aggregation or precipitation of components by adding the thickener. Therefore, a very low concentration, for example at 0.0005-0.3 wt. %, of carrageenan is effective which does not enhance the viscosity of the tea extracts. Carrageenan which contains 30-100 wt. % kappa-type carrageenan is preferable for the present invention.
Tea extracts which contain soluble solid matter at 0.2-18 Bx or so are preferably applicable to the present invention which include ones which are drunk without dilution and ones which are drunk after dilution.
The present invention also comprises, to enhance stability, 1) tea extracts which are obtained by chilling crude tea extracts prior to addition of carrageenan, followed by removing turbidness-giving components, 2) tea extracts which are obtained by adding tannase prior to addition of carrageenan, and 3) tea extracts which are obtained by adding tannase prior to chilling crude tea extracts, followed by chilling the crude tea extracts to remove turbidness-giving components.